Method of producing lead salts.



n. M. HARRINGTON.

METHOD 0F PRODUCING -LEAD SALTS.

APPLICATION FILED sEPLzI. |911.k

1,308,948. I l I Patented July 8, 1919.

luz/Emol?, RALPH M/fARF//v TU STATES PATENT OFFICE.

.RALPH M. HABBIN'G'TON, OF BROOKLYN, YORK, ASSIGNOB TO EINER A. SPERBY,

A OF BROOKLYN, NEW YORK.

I METHOD OF PRODUCING LEAD SALTS.

Specification of Letters Patent.

Patented July s, i919.v

To all 'whom z't may concern:

Be itknown that I, RALPH M. HARRING- TON, a citizen of the United States of America, residing at Brooklyn, in the county of Kings and State of New York, have invented certain new and useful Improvements in Methods of Producing Lead Salts, of which the following is a specification.

This invention relates to an improved method of making lead 'compounds electrolytically. More lspecic'ally it relates to the manufacture of compounds containing lead salts such as lead chromate, lead sulfate or lead carbonate by an electrolytic method.

I am aware that lead compounds have been produced, heretofore, by passing an electric current from a lead anode to a cathode through an anolyte capable of yielding a lead solvent and containing a soluble carbonate, and a similar catholyte and then carbonating the anolyte by adding carborn dioxid and causing` the desired product to vbe precipitated in the anolyte. I am also aware that it has been proposed to separate the anolyte and catholyte by means of a diaphragm in order to prevent lead compounds from reaching the cathode. Certain objections have appeared in manufacturing, according to this method, which have seriously limited its commercial exploitation.

By ,introducing the carbon dioxid, or other acid radical, into the catholyte, however, very important advantages are gained. For the sake of simplicity I will confine'the vfollowing disclosure to a method of manufacturing white lead although other lead compounds may be produced by the same method by usingacid radicals other than carbon dioxid, such as sulfuric or chromic acid, for example. The advantages, above referred to, may best be set forth by considering certain ofthe actions of the above described old method.

In this prior process the action is substantially as follows: Assuming that sodium acetatesolution is usedff'as the anolyte, lead ace-` uct 1s prec1p1tated 1n the anolyte and theV tate is formed at the anode. The carbonate in the anolyte reacts on the lead acetate to form white lead and obviously if the anolyte is high in carbonate the white lead is formed on and adheres to the anode thus seriously interfering 4with the operation of the system. Thus, with this old method, it is necessary to keep the anolyte low in carbonate and with this low -concentration'the anolyte is a poorfabsorber of 'carbon dioxid.

In my process I ass the carbon dioxid lnto the catholyte which is made'strongly alkaline so that the aboveobjection is and current density the composition of'both anolyte and catholyte remains practically constant, the rate of dil-fusion of the carbonate through the diaphragm being the same as the rate of formation inside the cathode compartment. Thus the percentagev of carbonate in the anolyte and also the product are under absolute control in my process which are very important advantages.-

It is also old inthe art to produce white lead by use of an electrolytic biuid cell, c'. e. one in which the catholyte and anolyte are kept separate by a diaphragm, and in which a solution of lead salt is formed in the anolyte.. In this process the anolyte and alkaline catholyte are withdrawn from the cell and mixed to produce lead hydroxid which is carbonated (outside the cell) to precipitate white lead. Or, as 'an alternative, the catholyte and anolyte are with-v drawn, the catholyte is then carbonated and the two then mixed to precipitate the white lead outside the cell.

Both of the last two described processes are open to many objections, among which are thefollowing. The process. is not continuous. made to prevent di'usion of the two fluids in the cell. The lead in solution in the Furthermore provision m-ust be anolyte increases to such a high value that A U there is danger of it depositing on the cathode unless lspecial precautions are taken.

lOn the other hand in my .process the prodas the invention is hereinafter developed.

Although my method is independent of the particular details of apparatus employed l. have found the apparatus illustrated diagrammatically in the drawing to be very convenient in carrying out the process.

Referring to the drawing it will be seen that a tank, or other fluid container, is provided. This tank is shown as containing an anode plate 2 and a frame 4. The frame 4, has mounted on each side thereof a suitable diaphragm 5, 5, such asparchment paper or vegetable parchment, forming a compartment for and containing the cathode 3` and catholyte. 'The diaphragms 5, 5 permit only a slow interchange of liquids by osmosis, and prevent solids passing therethrough.

The anode is a lead plate while the cathode may be of any conducting material such as iron, copper, etc. The tank l also contains the anolyte and the frame 4 thevcatholyte. Although lhave shown but one anode, cathode and frame a plurality may be provided if desired. .The tank 1 is shown as provided with a downwardly taperin portion V6 connected by means of a pipe to a settling tank 8. which in turn is provided with a pipe 10, at its upper portion, which terminates at the top of the tank 1. By operating a pump`9 shown in pipe line 7 the anolyte in tank 1 may be circulated in the following path: from tank 1, through pipe 7 into settling tank 8 and'through pipe l0 to the tank 1. Obviously any precipitate in the anolyte will settle to the bottom of tank 8 and may be drawn oi through the cock or valve 11 provided for that purpose. Furthermore by circulating the anolyte, it is kept uniform throughout.

Means are also shown for circulating the catholyte solution. A pipe 12 terminates at one end and near the bottom of frame 4 and at its other end at the bottom of a carbonating tower 16. A pipe 13 connects the u per part of frame 4 and the upper partJ o the carbonating tower 16. A pump 15 is placed in line 12 to circulate the catholyte along the following path: from frame 4, through pipe 13, down through tower 16 and then through pipe 12 to the bottom of the frame 4. The rate of circulation of the catholyte through the tower 16 may be controlled by a valve 14 in pipe 12 orby means of a valve 17 located in a by-pass 18 around the tower. The carbon dioxid is introduced through pipe 19 and travels upwardly, through a quantity of coke, 25 or the like which may be provided in the tower, and then exhausting at 24.

Flue gas contains carbon dioxid and may Y therefore be used in carbonating the catholyte. Before introducing this gas through pipe 19 I prefer to purify it by passing it through a scrubber 20 charged with -limestone 26 or like substance and through which a-current of water is passed from p1pe`21 to pipe 22. The ue gas enters through pipe ate, such as'sodium carbonate, or a small amount of lead acetate may be added.

The catholyte solution comprises the same alkali metal salt; for example, sodium acetate, as the anolyte and in addition preferably contains a soluble carbonate, or hydrate or mixture of these. Thus sodium carbonate or bicarbonate may be employed. The caiholyte, as mentioned before, is made more strongly alkaline than the anolyte.

Assuming that the above suggested compounds are employed, that a source of E. M.

F. is connected across the plates, that flue gas is supplied at 23 and that both the catho lyte and anolyte are circulating the action is probably as follows:

The sodium acetate reacts with the lead plate to form lead acetate. Thus:

At' the cathode, sodium reacts with water to form sodium hydroxid, thus:

Na-i-HZO :NaOH-l-H.

The sodium hydroxid reacts with the carbon dioXid, in the carbonating tower 16, to form more or less sodium carbonate, thus:

The sodium carbonate thus formed in the catholyte reaches the anolyte by diffusing through the diaphragms 5, or by overflowing, and reacts with lead acetate to precipitate white lead, thus:

The white lead is precipitated in the anolyte by such a dilute solution of sodium carbonate that there is no danger of it adhering to the anode surface.

It will be noted, on inspection of the last equation, that sodium acetate is regenerated, so that the. process is not only` continuous but also cyclic. The vonly materials consunied are water, carbon dioxid (flue gas) and lead. The precipitated white lead will settle in' tank 8 and may be drawn olf at 11.

In order to produce White lead similar to that produced by the Dutch process both large and small particles must be produced. Electrolytic white lead comparatively low in carbonate consists of very fine amorphous particles while that comparatively' high in carbonate consists of muchV larger more or less crystalline particles. A pro er combination of these gives a white lea of minimum oil absorption and i high covering at least partiall power. Thus by `regulating the amount of carbon dioxid supplied to the catholyte the character and quality of the product may be controlled. This regulation may be effected either by adjusting the valve 14 or the valve 17 either of which will control the amount of catholyte subjected to the carbon dioXid.

Having described my invention what I desire to secure by Letters Patent is:

1. The method of producing a lead compound electrolytically which comprises passing an electric current from a lead anode to a cathode through an electrolyte capable of yielding a lead solvent, substantially excluding lead compounds from said cathode `by a diaphragm and introducing into the catholyte an acid capable of yielding an insoluble precipitate with lead when it reaches the anolyte within the cell.

2. The method of producing a lead compound electrolytically which comprises producing. an alkaline hydrate at the cathode, at least partially neutralizing this hydrate by an 'acid ca able of yielding an insoluble precipitate with lead and introducing the alkali salt thus formed into the anolyte within the cell. l

3. The method of producing a lead compound electrolytically which comprises producing an alkaline hydrate at the cathode, neutralizing this hydrate 'by an acid capa le of yielding an insoluble precipitate with lead and introducing the 'alkali salt fthus formed into the anolyte to an extent substantially necessary to prevent lead forming in solution.

4. The method of producing a lead com pound electrolytically which comprises prof ducing an alkali hydrate at-the cathode, at

- thus formed into the anolytewithin the cell.

least partially neutralizing this hydrate by an acid'capable of yielding an insoluble recipitate with lead, and introducing the al ali salt thus formed into the anolytewithin the cell. at substantially the same rate at' which it forms in the. catholyte.

5. The method of producing a lead compound electrolytically which 'comprises producing an alkaline hydrate at'the cathode, at least Vpartially neutralizing this Y vhydrate by an acid capable of ielding .an insoluble precipitate with lea thus producing an alkali salt, precipitating the desired lead compound in the anolyte Within the cell by introducing the alkali salt into the latter, circulating the anolyte and removing thepecipitate from the anolyte at a place exterior to the electrolytic cell.

6. The method of producing a lead corn- -pound electrolytically which comprises producing an alkaline hydrate at the cathode, circulating the catholyte, introducing an acid radical into saidy catholyte exteriorly tothe cell and introducing the alkali Salt 7. The .method of producing white lead alkaline than the anolyte.

electrolytically which comprises. producing an alkaline hydrate at the cathode, carbonat ing the alkaline hydrate in the catholyte and introducing the alkali carbonate .thus formed into a weakly alkaline or neutral anolyte by osmosis.

9. The method of producing white lead electrolytically which comprises producing an alkaline hydrate. in acomparatively strongly alkaline catholyte, carbonating the alkaline hydrate in the catholyte and intro-l ducing the alkali carbonate thus formed into a comparatively weakly alkaline anolyte by osmosis.

10. The method of producing white lead electrolytically which comprises producing an alkaline hydrate in a comparatively strongly alkaline catholyte, carbonatingthe alkaline hydrate in the catholyte and introducing the alkali carbonate thus formed into a comparatively weakly alkaline anolyte .through a diaphragm, the catholyte being maintained at least fifty times more strongly 11. The method of forming a lead salt away from'the surfaceA of the lead anode of a biluid electrolytic cell which comprises dissolving the anode and precipitating theJ lead salt by introducing the precipitating reagent irs-t into the catholyte and then int the anolyte by osm'osis.

12. The method of forming a lead salt away from the surface of the lead anode of a biluid electrolytic cell which comprises dissolving the anode and precipitating the lead l salt by introducing the precipitating re-l agent rst intothe catholyte and then into the anolyte through a diaphragm. Y

13. The method of producing a precipi-l tate in the anolyte of a biuid electrolytic vcell which. comprises introducing the precipitating agent from the catholyte, by osmotic action into the anolyte.

14. In a paratus for the production of l white lead y electrolysis,.a container adaptedl to contain a lead anode anda metallic cathode, a parchment compartment therein to separate the -cathol te from the anolyte, a settling tank or the white lead precipitate, means for continuously circulating the anolyte through vthe container and tank, a mixing chamber, a source vof supply of a gaseous acid radical for supplying said gas to said chamber'and means for continuously circulating the catholyte through said compartment and chamber.

15. In apparatus for the'production of white lead by electrolysis, ai. container adapted toV contain a lead anode and a metallic cathode, a parchment compartment therein to separate the catholyte from the anolyte, a settling tank for the White lead precipitate, means for continuously" circulating the anolyte through the container and tank, -a mixing chamber, a source of supply of a gaseous acid radical for supplying said gas to said chamber, means for continuously circulating the catholyte through said compartment and chamber and 'a regulatable by-pass around said chamber.

16'. The method of forming white lead away from the surface of the lead anode of a biiiuid electrolytic cell which consists in circulating the anolyte around a path through and exterior to the cell, collecting the white lead exterior to the cell, circulating the catholyte around a separate similar path and introducing the acid radical to said catholyte exterior to the cell.

17. The method of producing white lead electrolytically which comprises producing an alkaline hydrate at the cathode, carbonating the alkaline hydrate in the cathol and introducing the alkali carbonate t us formedinto a weakly alkaline anolyte an alkaline hydrate at the cathode, carbon"- Y ating the alkaline hydrate in the catholyte and introducing the alkali carbonate thus formed into a weakly alkaline anolyte by osmosis, the rate of carbonating being so proportioned that the White lead is precipitated between the anode and diaphragm, and

the carbonate passes through the diaphragm at substantially the same rate as formed' whereby the composition of the electrolyte remains substantially constant.

In testimony whereof I have aiixed my signature.

RALPH M. HARnI-NGTON. 

